The aircraft departed Haverfordwest Airport in Wales at 16.00 hrs en-route to Taghmon in Co. Wexford.After approximately 55 minutes flying time the engine stopped without warning.The Pilot immediately selected the other fuel tank and attempted to re-start the engine.With the aircraft descending through 900 ft the restart attempt was abandoned and a successful ditching was carried out.The Pilot was not injured.The Investigation found that the engine stopped probably due to fuel starvation relating to a fuel-vapour related problem.